1. Field of the Invention
The present invention relates to a technique for miniaturizing semiconductor integrated circuits. The invention disclosed in this specification includes in its scope an element formed using a compound semiconductor, in addition to that formed using a silicon semiconductor, as a component of a semiconductor integrated circuit, and discloses an element formed using a wide-gap semiconductor as an example.
In this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
Oxide semiconductors have recently attracted attention as materials for next-generation thin film transistors. Examples of oxide semiconductors include tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like, and there are known thin film transistors in which such oxide semiconductors are used in channel formation regions.
Examples of oxide semiconductors include not only a single-component metal oxide but also a multi-component metal oxide. In particular, an In—Ga—Zn—O-based oxide material (hereinafter also referred to as IGZO) has been actively studied. Crystal structures of IGZO were found in 1985 by Kimizuka, Nakamura, Lee, et al. from National Institute for Research in Inorganic Materials, and Non-Patent Document 1 shows that IGZO has homologous structures represented by InGaO3(ZnO)m (m=1 to n).
It has also been confirmed that an oxide semiconductor including such IGZO can also be applied to a channel formation region of a thin film transistor (see, for example, Patent Document 1).
In addition, in Patent Document 2, the off-state current of a transistor formed using an oxide semiconductor including IGZO (L/W=10 μm/50 μm) is calculated to be 100 zA/μm or less.    [Patent Document 1] Japanese Published Patent Application No. 2007-123861    [Patent Document 2] Japanese Published Patent Application No. 2011-171702